The present invention generally relates to a small-sized dielectric resonator apparatus, and more particularly, to a dielectric resonator using a TE.sub.01.delta. mode.
Generally, dielectric resonators may comprise resonators which are smaller in size and higher in Q as compared with the conventional metallic cavity resonators. Note for example, the dielectric resonator apparatuses which are used as band-pass filters in transmitter multiplexers or the like in microwave communication apparatuses.
The construction of a dielectric resonator varies in accordance with the electromagnetic wave mode being used, with a particular mode being used in accordacne with a particular object. For example, in the TE.sub.01.delta. mode, which is not very good with respect to spurious characteristics, the degree of energy concentration of the resonator is high, and the loss of the entire resonator is determined only by the loss of the dielectric resonator, so that a higher Q may be provided. In the case of the TEM mode, the spurious characteristics are good, but the loss of the metallic conductor is comparatively large, whereby the Q of the resonator is not so high. Although the TM mode advantageously shows intermediate characteristics between these two modes, the conductivity of the splicing face has to be properly retained, because an actual current flows across the splicing face between the dielectric resonator and its case. For this purpose, it is necessary to absorb any mechanical distortion which is caused by the difference between the thermal expansion coefficient of a dielectric resonator made of ceramics and that of a case, so metallized ceramics are required to be used as the material of the case.
In view of the preceding metal, which is superior to treat, is used as the case. In order to improve a Q, the dielectric resonator of the TE.sub.01.delta. mode is used.
In a dielectric resonator using the conventional TE.sub.01.delta. mode, a cylindrical dielectric resonator, which is made of, for example, TiO.sub.2 system ceramic material, is secured on a cylindrical support stand within a closed metallic case. As this type of dielectric resonator uses dielectric ceramics as described hereinabove, it may be smaller than a metallic cavity resonator. As the electromagnetic energies are fully concentrated within the dielectric resonator, resonator with the higher Q may be constructed.
Conventionally, when a band-pass filter is constructed with a plurality of these dielectric resonators arranged within the same case, the above-described cylindrical dielectric resonators are inductively coupled in the lateral direction, being arranged in one plane within the metallic case. A filter arranged according to this method has disadvantages in that asymmetrical modes such as EH.sub.11.delta., TM.sub.01.delta., HE.sub.11.delta., etc. are likely to be excited, and the spurious characteristics are inferior.
In another known dielectric resonator apparatus, a plurality of cylindrical dielectric resonators, are ideally located along the central shaft of each dielectric resonator and are arranged in the central axis direction. FIG. 27 is a partially broken away perspective view showing the construction of the apparatus. In FIG. 27, the cylindrical dielectric resonators 21, 22, 23, 24 are each secured by a ring-shaped spacer 31 within the metallic case 30.
Another known dielectric resonator apparatus includes fan-shaped partial cylindrical dielectric resonators, and uses the symmetrical property of the electromagnetic wave mode to make the whole apparatus smaller in size, and improved in radiation property. FIG. 28(A), and FIG. 28(B) are respectively a top view and a front view showing the inside construction of the apparatus. In FIG. 28, the cylindrical dielectric resonators 51 through 54 are cut in half by a plane containing the central axis thereof, with the cut face being secured in contact against the metallic case 40. Reference characters 43, 45 show input, output connectors, and reference characters 42, 44 show rods which provide the coupling circuit.
In the conventional dielectric resonator apparatus shown in FIG. 27, the above-described asymmetrical mode is hard to excite, and the spurious characteristics are good, but it also has diadvantages, in that the reliability is lower in terms of strength if synthetic resin is used as a spacer 31, and the unloaded Q, i.e., Q.sub.0 is lower because of low tan .delta.. The thermal expansion coefficient of the metallic case 30 is considerably different from that of the spacers when ceramic material is used as the spacers, and it is difficult to absorb the mechanical distortion caused by the thermal expansion. In the dielectric resonator apparatus shown in FIG. 28(A), (B), each of the dielectric resonators is in contact against the inner wall of the metallic case without any interval therebetween, so that the whole is smaller in size and the radiation effect becomes higher. However, as in the conventional dielectric resonator apparatus wherein a plurality of cylindrical dielectric resonators are arranged along a plate, the asymmetrical mode is likely to be excited, the spurious characteristics are inferior, and furthermore the design property is worse.